In general, a particle beam therapy system is provided with a beam generation apparatus that generates a charged particle beam, an accelerator that is connected with the beam generation apparatus and accelerates a generated charged particle beam, a beam transport system that transports a charged particle beam that is accelerated by the accelerator so as to gain predetermined energy and then emitted, and a particle beam irradiation apparatus, disposed at the downstream side of the beam transport system, for irradiating a charged particle beam onto an irradiation subject. In order to irradiate a charged particle beam onto an irradiation subject at an arbitrary angle, a particle beam irradiation apparatus is disposed in a three-dimension-irradiation rotating gantry.
Patent Document 1 discloses a particle beam irradiation apparatus installed in a building covered with a concrete radiation shielding material. The particle beam irradiation apparatus disclosed in Patent Document 1 is a rotating gantry; this rotating gantry is provided with a treatment table on which a patient lies, an irradiation unit that irradiates a proton beam onto a patient, and an introduction line that introduces a proton beam, which is guided by a guide line, into the irradiation unit. In this rotating gantry, in order to ensure the balance between the introduction line and a stand, counter weights are arranged at the positions that are on the outer circumferential surface of a cylinder portion and face each other with respect to the rotation axis.